Method of false-twisting multifilament yarn

ABSTRACT

The multifilament yarn produced by this method has a highly crimped or curled configuration and very little torque. The yarn is threaded about the exit pin of a false-twist spindle by a slip-knot type of loop which prevents passage of the twist from one side to the other of the exit pin and permits a relatively high number of turns of false-twist to be inserted in the yarn, on the order of from about 150 to 185 turns per inch. Fabric knit of this yarn, such as ladies&#39;&#39; sheer hosiery, panty hose, and the like, has a creped appearance when relaxed with a high degree of stretchability and recoverability.

United States Patent Fain [ 1 June 6, 1972 [54] METHOD OF FALSE-TWISTING MULTIFILAMENT YARN [21] Appl.No.: 81,205

[5 6] References Cited UNITED STATES PATENTS 3,210,964 10/1965 Russell ..57/157 TS Koizumi ..57/157 TS Comer et a] ..57/157 TS Primary Examiner-John Petrakes Attorney-Parrott, Bell, Seltzer, Park & Gibson The multifilament yarn produced by this method has a highly crimped or curled configuration and very little torque. The yarn is threaded about the exit pin of a false-twist spindle by a slip-knot type of loop which prevents passage of the twist from one side to the other of the exit pin and permits a relatively high number of turns of false-twist to be inserted in the yarn, on the order of from about 150 to 185 turns per inch. Fabric knit of this yarn, such as ladies sheer hosiery, panty hose, and the like, has a creped appearance when relaxed with a high degree of stretchability and recoverability.

6 Claim, 9 Drawing Figures PATENTEBJUH 6|972 3,667,209

SHEET 10F 2 INVENTOR! EBOBBY RAY Fm N E \0 g I 8W ATTORNEYS v PATENTEDJUH 6 I972 SHEET 2 or 2 1 BOBBY RAY FAJN zw-zwa /gwv g lzw ATTORNEYS METHOD OF FALSE-TWISTING MULTIFILAMENT YARN This invention relates generally to a method of producing a highly crimped or curled multifilament yarn on a false-twist machine and more particularly to a method of producing a yarn having a relatively high number of turns of false-twist therein to provide enhanced stretchability and recoverability to a fine gauge fabric knit of the yarn, such as ladies hosiery, panty hose, and the like.

Many different false-twisting methods have been proposed for imparting crimp or curl to multifilament thermoplastic yarn to impart latent torsional stresses and torque to the yarn so that it has a strong tendency to crimp and curl, particularly when a fabric knit therefrom is subjected to heat. When knit in fine gauge hosiery articles, these yarns impart a sufficient amount of stretch to the fabric that it will cling to the leg but the recoverability or snap-back is limited, particularly after having been stretched to near its stretch limit, as when the fabric in the knee area is stretched when the leg is bent.

In attempts to overcome this problem, the number of turns of false-twist has been increased up to above 100 turns per inch. However, this increase in the number of turns of falsetwist has created other problems. For example, this high number of turns makes it difficult to maintain a uniform twist in the yarn as it passes through the heating zone so that it is impossible to uniformly crimp the yarn particularly when the yarn is false-twisted above about 125 turns per inch.

With the foregoing in mind, it is an object of the present invention to provide a method of producing a uniformly crimped multifilament yarn having enhanced stretchability and improved stretch recovery by imparting a high number of turns of false-twist to the yarn on a conventional type of falsetwist machine.

According to a preferred embodiment of the present invention, the multifilament yarn is threaded about the exit pin of a false-twist spindle with a slip-knot type of loop so that the relatively high number of turns of false-twist imparted to the yarn in advance of the spindle, within the range of about 150 to 185 turns, is constantly maintained in the heating zone. The method of this application is particularly adapted for use with low denier yarns of the type usually employed in knitting ladies fine gauge seamless hosiery, panty hose, and the like, not over about 40 denier. When knit, the individual filaments of the multifilament yarn tend to separate and crimp or curl and form reversing coils or loops which somewhat offset or balance the torque which normally occurs in a yarn having been subjected to a high number of turns of false-twist. While the yarn has a sufficient amount of torque that it is preferable that the hosiery articles be knit with alternate courses of yarns which have been false-twisted in opposite directions, the stretch in the fabric is not derived from the torque in the yarn but rather from the very small crimps or curls which form in the individual filaments when the fabric is relaxed.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds which when taken in connection with the accompanying drawings, in which I FIG. 1 is a somewhat schematic isometric view of one station of a false-twist machine and illustrating the yarn being produced in accordance with the present invention;

FIG. 2 is a greatly enlarged isometric view of the upper exit end of the false-twist spindle, illustrating the first step in threading the yarn around the exit pin in accordance with the present invention;

FIGS. 3, 4 and 5 illustrate the subsequent steps in the threading operation;

FIGS. 6 and 7 are further enlarged views of the upper ends of separate false-twist spindles illustrating the manner in which yarns are reversely looped about the exit pins for processing of the yarns in opposite directions to produce opposite torques in the yarn;

FIG. 8 is an isometric view of a panty hose garment knit of the yarns processed in accordance with the present invention;

and

FIG. 9 is a greatly enlarged view of a small area of the leg portion of the panty hose, taken in the dotted line rectangle in FIG. 8 and showing the manner in which the yarns in the stitch loops form small crimps and curls when the fabric is partially relaxed.

The present invention is particularly concerned with the method of false-twisting multifilament yarns which fall within the range of those yarns normally used in knitting ladies sheer hosiery and the like, for example, within the range of about 7 to 40 denier. The multifilament yarns most frequently used in this range include 12/2, 14/2, 15/3, 15/5, 17/2, 17/3, 18/2, 18/3, 20/6, 20/7,and 40/17 deniers. As has been pointed out, it is necessary that the multifilament yarn be threaded about the exit pin of the false-twist spindle with a slip-knot type loop so that the yarn may be false-twisted with a relatively high number of turns of false-twist, within the range of about to turns per inch.

Referring to the drawings, FIG. 1 schematically illustrates one station of the preferred type of false-twist machine on which the yarn is processed in accordance with the present invention. The false-twist machine illustrated is of the type known as the Model 551 false-twist machine, manufactured by Leesona Corporation. Although only one station is illustrated, it is to be understood that the machine is provided with closely spaced false-twisting stations along each side. A single end of yarn Y is withdrawn from a yarn supply pirn 10 which is suitably supported on the lower portion of the machine. The yarn Y is preferably in the raw" condition received from the yarn producer and usually contains a relatively low amount of twist, on the order of about one-half to three-quarters of a turn per inch of what is known as producers twist."

The yarn Y is drawn upwardly and through a guide wire 11 supported on a guide support rod 12 and then through a sinuous wire guide 13 which is attached to the leading portion of a support plate 14. The yarn Y then passes around a post 15 and around a small V-grooved guide wheel 16 which is provided with suitable ball bearings to facilitate rotation thereof. The yarn Y is wrapped about the guide wheel 16 in a counterclockwise direction and then passes beneath a yarn guide wire 17 and is wrapped several turns about a lower feed roll 20. The yarn then passes upwardly through a groove 21 in a heater plate 22, through yarn guide wires 23 and 24, and upwardly through a false-twist spindle 25 which is rotated by a drive belt 26. The yarn is looped about the exit pin of the falsetwist spindle 25 in a special manner, to be presently described.

From the false-twist spindle 25, the yarn is directed upwardly over a guide rod 27, through a traversing yarn guide 28 and taken up on a take-up bobbin 30. The take-up bobbin 30 is rotated at the desired speed, relative to the feed roll 20 and the rotational speed of the false-twist spindle 25, by means of a cork drive roll 31, the outer peripheral surface of which engages the surface of the take-up bobbin 30 and the yarn wound thereon to provide a surface-to-surface drive.

As shown in FIGS. 2-6, the upper end of the false-twist spindle 25 is provided with a small exit pin 32 which is tapered inwardly toward the center from each end and which is formed of a hard ceramic material, such as Alsimag. The diameter at the central portion of the pin 32 is preferably small, on the order of 0.030 of an inch.

As is well known, it is the usual practice to simply wrap the yarn one or more times around the exit pin 32 in threading up the machine. In order to prevent slippage of the twist past the pin and to permit the high number of turns of false-twist to be inserted in the yarn, the yarn is threaded or looped about the exit pin 32 in a special slip-knot type of loop. This loop is formed by first drawing the yarn upwardly through the falsetwist spindle 25 by means of the usual threading hook, the end of which is indicated at 34 in FIG. 2, and the spindle 15 is rotated so that the yarn is positioned behind the exit pin 32 (FIG. 2). The threading hook 34 is then passed beneath the false-twist exit pin 32 to engage the yarn and then drawn forwardly, as illustrated in FIG. 3, to form a loop, indicated at L. The free end portion of the yarn Y is then passed through the loop L, either from left to right as illustrated in FIG. 4, or from right to left, depending upon the direction in which the spindle 25 is to be rotated. The spindle 25 shown in FIGS. 2-6 is to be rotated in a counterclockwise direction, looking downwardly thereon, so that torque is imparted to the yarn in a 2 direction.

The free end portion of the yarn Y is then drawn upwardly, over the guide rod 27, passed through the traverse guide 28, and onto the corresponding take-up bobbin 30. The yarn is thus drawn down and around the exit pin, as shown in FIGS. and 6. Because of the size of FIGS. 25, the single end of yarn has been illustrated as a monofilament, however, it is to be understood that this single end of yarn includes a plurality of filaments, usually from two to about seven filaments.

The false-twist spindle 25 is rotated in a clockwise direction, as illustrated in FIG. 7 and the yarn Y is threaded about the false-twist pin 32 with a slip-knot loop formed in an opposite direction to produce a yarn having an opposite torque from that produced when the spindle is rotated in the counterclockwise direction, illustrated in FIG. 6. The yarn is oppositely threaded by passing the free end portion through the loop L from right to left and in the opposite direction from that illustrated in FIG. 4 so that when the loop is tightened (FIG. 7) the running bight of the loop L rubs across and around the portion of the yarn Y leaving the pin from right to left.

On the other hand, the running bight of the loop L in FIG. 6 rubs across and around the portion of the yarn leaving the exit pin 32 from left to right. In either slip-knot loop, the yarn passes upwardly on one side of the exit pin 32 and then downwardly on the same side of the exit pin to form a looped portion in the yarn. The yarn then passes down around and beneath the exit pin and upwardly on the opposite side of the exit pin and through the looped portion as it leaves the exit pin. The manner in which the yarn is threaded around the exit pin of the fals etwist spindle prevents twist from passing from one side of the exit pin to the other and provides an efficient twist trap so thata relatively high number of turns of falsetwist may be imparted to the yarn. The tension in the yarn above the false-twist spindle 25 is preferably maintained at a relatively low level, about grams, while the heat applied to the running yarn is preferably maintained within the range of about 360 to 430 F.

EXAMPLE As an illustrative, but non-limiting example, very satisfactory yarn has been produced in accordance with the present method for use in knitting the leg portion of ladies panty hose, as set forth in the following specific example. Single ends of l5/3 denier nylon yarn Y and Y are false-twisted on spindles rotating in opposite directions and with the yams being looped about the exit pins in opposite directions, as illustrated in FIGS. 6 and 7. The temperature of the heater block 22 is maintained at 370 F. The false-twist spindle is rotated at 147,000 r.-p.m., the speed of the take-up bobbin 30 and the feed roll are adjusted to impart I66 turns of false-twist per inch to the yarn while about 15 grams of tension is maintained on the yarn from the spindle to the take-up bobbin 30.

The yarn produced in accordance with the above example is particularly adapted for knitting the leg portion and foot portions of ladies seamless panty hose, such as indicated at H in FIG. 8. The elongate stocking blanks are knit on conventional circular hosiery knitting machines and the upper ends are slit and the slit edges are sewn together to form the body portion. The panty hose are then finished in the usual manner which may include preboai'ding, dyeing, scouring, and then final boarding, which may include dyeing, scouring, and boarding in a single operation, or which may include dyeing and developing the crimp in the yarn without boarding. As illustrated in FIG. 9, the four courses C-l through C-4 and four wales WI through W-4 clearly illustrate the manner in which the individual filaments in the alternately knitted yarns Y and Y crimp and curl when the fabric is partially relaxed. The individual loops are very small, on the order of about one-third of the length of one leg of each stitch loop. When the fabric is completely relaxed, the filaments crimp and coil orloop to a much greater extent than shown in FIG. 9 and the knit stitch loops completely disappear.

The full elasticity and distortion of the yarn in the stitch loops is developed without requiring excessive agitation of the fabric during the finishing steps and the yarn in the finished stocking has only slight torque but in individual filaments have a very strong tendency to crimp and coil or loop. The distortion of the yarn, looping and curling and the generally distorted condition of the individual filaments of each yarn is illustrated in FIG. 9. As shown in FIG. 9, some of the stitch loops are larger than others and the stitches of the yarns therein are distorted in anirregular manner. In addition to the distortion shown, the stitch loops are also distorted in the plane toward and away from the observer.

When the fabric is stretched, the separated filaments are drawn together and loops therein straighten out so that the fabric is stretchable in both walewise and coursewise directions. Upon relaxation of the fabric, the yarns have a strong tendency to return to their looped and curled condition to provide enhanced stretch recovery or snap-back which is a particularly desirable characteristic in ladies panty hose where the upper portion of the garment is supported in a substantially fixed position around the waist of the wearer.

In the drawings and specification there has been set forth a preferred embodiment of the invention and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

I claim:

1. A method of producing a highly crimped plural filament yarn on a false-twist machine having a false-twist spindle with an exit pin, said method comprisingthe steps of a. withdrawing a single end of plural filament thermoplastic synthetic yarn of not over about 40 denier from a single yarn supply source,

b. false-twisting the single end of yarn with a relatively high number of turns of false-twist, within the range of about 150 to I turns per inch,

0. heat-setting the twisted yarn in advance of the false-twist spindle, and while (I. passing the yarn through a slip-knot loop formed about the exit pin to prevent passage of the twist from one side to the other of said exit pin and to permit said high number of turns of false-twist to be inserted in the yarn in advance of said spindle, and then e. taking up the single end of false-twisted yarn on a take-up bobbin.

2. A method according to claim 1 wherein said yarn includes from two to seven filaments.

3. A method according to claim 2 wherein each of said filaments is not over about 10 denier.

4. A method according to claim 1 wherein said twisted yarn is heat-set by passing it over a heater plate maintained between about 360 to 430 F.

5. A method according to claim 4 wherein said yarn is heatset by passing it over a heater plate maintained at about 370 F 6. A method according to claim 1 wherein said yarn is 15/3 nylon and is false-twisted with about 166 turns per inch. 

1. A method of producing a highly crimped plural filament yarn on a false-twist machine having a false-twIst spindle with an exit pin, said method comprising the steps of a. withdrawing a single end of plural filament thermoplastic synthetic yarn of not over about 40 denier from a single yarn supply source, b. false-twisting the single end of yarn with a relatively high number of turns of false-twist, within the range of about 150 to 185 turns per inch, c. heat-setting the twisted yarn in advance of the false-twist spindle, and while d. passing the yarn through a slip-knot loop formed about the exit pin to prevent passage of the twist from one side to the other of said exit pin and to permit said high number of turns of false-twist to be inserted in the yarn in advance of said spindle, and then e. taking up the single end of false-twisted yarn on a take-up bobbin.
 2. A method according to claim 1 wherein said yarn includes from two to seven filaments.
 3. A method according to claim 2 wherein each of said filaments is not over about 10 denier.
 4. A method according to claim 1 wherein said twisted yarn is heat-set by passing it over a heater plate maintained between about 360* to 430* F.
 5. A method according to claim 4 wherein said yarn is heat-set by passing it over a heater plate maintained at about 370* F.
 6. A method according to claim 1 wherein said yarn is 15/3 nylon and is false-twisted with about 166 turns per inch. 